Engine systems may be configured with boosting devices, such as turbochargers or superchargers, for providing a boosted aircharge and improving peak power outputs. The use of a compressor allows a smaller displacement engine to provide as much power as a larger displacement engine, but with additional fuel economy benefits. However, compressors are prone to surge. For example, when an operator tips-out of an accelerator pedal, an engine intake throttle closes, leading to reduced forward flow through the compressor, and a potential for surge. Surge can lead to noise, vibration, and harshness (NVH) issues such as undesirable noise from the engine intake system. In extreme cases, surge may result in compressor damage. To address compressor surge, engine systems may include a compressor recirculation valve (CRV) coupled across the compressor to enable rapid decaying of boost pressure. The CRV may recirculate compressed air from the compressor outlet to the compressor inlet allowing a decrease in pressure at the compressor outlet.
The CRV may comprise a throttle and a position sensor for indicating a change in a position of the throttle of the CRV. As such, the CRV may degrade with use over time. For example, the throttle of the CRV may be stuck at a given position and may not move when commanded. In one example, the throttle may be stuck in a fully open position. Alternatively, the throttle may be lodged in a fully closed position. In yet another example, the throttle may be stuck at a position in-between the fully closed and fully open positions. An example approach to verify if the CRV is stuck in an open position is shown by Wegener et al. in U.S. Pat. No. 7,926,335. Herein, changes in charging pressure in response to a triggering of the CRV are analyzed. Specifically, the CRV may be diagnosed to be stuck in a mostly open position if the charging pressure downstream of the intake compressor does not increase as expected when the CRV is triggered to a closed position. U.S. Pat. No. 7,926,335 primarily identifies a CRV that is stuck in an open or mostly open position.
The inventors herein have identified a potential issue with the above approach. As an example, variations in charging pressure may be due to factors other than a change in position of the CRV throttle. For example, charging pressure may fluctuate due to modifications to pedal position (e.g. accelerator pedal), changes in gear, spark timing changes, etc. Noise from these and other parameters may influence charging pressure. Accordingly, variations in charging pressure in response to a triggering of the CRV cannot be exclusively ascribed to a change in CRV position.
The inventors herein have recognized the above issue and identified an approach to at least partly address the issue. In one example, a method for a boosted engine comprises commanding a periodic signal command to a compressor bypass valve (CBV), and indicating degradation of a throttle of the CBV based on changes in pressure at an inlet of an intake throttle in response to a the periodic signal command. In this way, CRV throttle degradation may be specifically identified.
For example, an engine system may include a compressor having a compressor recirculation passage coupling an outlet of the compressor to the compressor inlet. In alternate embodiments, the recirculation path may couple an outlet of a charge air cooler to the compressor inlet. Flow through the recirculation path may be controlled via a compressor recirculation valve (CRV). The CRV may be a continuously variable compressor recirculation valve (CCRV). An engine controller may be configured to adjust a position of the CRV based on changes in airflow through an intake throttle so as to reduce compressor surge. Further, the engine controller may receive feedback regarding changes in throttle inlet pressure (TIP) from a throttle inlet pressure sensor located upstream of the intake throttle and downstream of the compressor. In order to determine if the CRV is degraded (e.g. stuck in a given position), TIP may be measured in response to a commanded change in position of the CRV. To ensure that TIP readings are minimally affected by noise factors, the command may include a periodic signal. In one example, the periodic signal may be a square waveform signal. If variations in TIP substantially correspond to the periodicity of the commanded periodic signal, the CRV may not be degraded (e.g. not stuck). However, if changes in TIP do not substantially match the periodic pattern of the commanded periodic signal, the CRV may be diagnosed to be degraded.
In this way, CRV degradation may be determined in a more reliable manner. By commanding a periodic signal with a specific periodicity, influence of noise factors on throttle inlet pressure (or charging pressure) may be reduced. Further, a more accurate determination of degradation in the CRV, particularly degradation of CRV throttle, may be realized. Further still, by isolating the degradation to a specific component of the CRV, diagnosis and repair expenses may be reduced. Overall, maintenance of the engine may be enhanced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.